ps7s05a - MIT Department of Biology 7.013: Introductory...

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MIT Department of Biology 7.013: Introductory Biology - Spring 2005 Instructors: Professor Hazel Sive, Professor Tyler Jacks, Dr. Claudette Gardel 7.013 Spring 2005 Problem Set 7 FRIDAY May 6th, 2005 Question 1 Bovine spongiform encephalopathy (BSE, also called mad cow disease) and other similar diseases are caused by infectious particles called prions. a) Prions are made of (circle one.) Viruses bacteria DNA RNA protein lipid carbohydrate b) True or false, if false correct the sentence: T F Several new mutations arise in the brains of cows that become affected by BSE. Affected and unaffected cells are genetically identical. T F In BSE, viral factors convert proteins in the brain from one form to another. Protein conformational changes occur without contribution from an external pathogen. BSE cannot be transmitted from one cow to another. T F BSE can be transmitted between cows by injection or ingestion of affected CNS material. T F Spongiform encephalopathies cannot be transmitted from one species to another. These diseases are not spread as easily between species as among animals of the same species, but at low frequency they can jump the species barrier. In yeast, there have been found prions that behave similarly to those that cause BSE. In the case of one yeast prion, one protein conformation causes the cells to be white and another conformation causes them to be red. This confers to colonies being red or white. Assume that the protein state analogous to the infectious form of BSE causes the yeast to be red. You grow these yeast and you notice that individual colonies are mostly of a single color, but small white sectors arise within red colonies, and small red sectors arise within white colonies. c) What causes red sectors to arise within white colonies? Some protein spontaneously converts to the prion form. d) If you took yeast from a red sector and replated them what color colonies would form and why? Red. Once some of the prion form has been generated, it will mostly be stably maintained in the population. So there will be red colonies with some occasional white sectors. e) What causes white sectors to arise within red colonies?
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Some cell division events result in cells that did not inherit any of the prion form of the protein. . The prion is inherited as a cytoplasmic factor.
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This note was uploaded on 11/11/2011 for the course BIO 7.012 taught by Professor Lander during the Fall '10 term at MIT.

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ps7s05a - MIT Department of Biology 7.013: Introductory...

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